November 8, 2012

Crocodiles And Alligators Are Actually Sensitive Creatures

Crocodiles and alligators are well-known for being cold-blooded and having thick skin, but new research from a pair of Vanderbilt University scientists has shown that the ancient reptiles can be quite sensitive.

More specifically, the scientists demonstrated that these reptilian predators have small pigmented domes that dot their skin-- conveying a sense of touch is even more responsive than that of humans, according to the pair´s report in the Journal of Experimental Biology.

"We didn't expect these spots to be so sensitive because the animals are so heavily armored," said study co-author Duncan Leitch, a graduate student at Vanderbilt.

Previous studies have noted these spots before and have dubbed them "integumentary sensor organs" or ISOs. A variety of different hypotheses were made about their possible function, including being a glandular source of oily secretions, detectors of electric fields, or the ability to gauge water salinity.

The Vanderbilt duo´s study was heavily influenced by a 2002 study from a biologist at the University of Maryland. That study found alligators in a darkened aquarium detected droplets of water even while their hearing was disrupted by white noise. The Maryland biologist asserted that the sensor spots on the animals´ faces allowed them to detect the disturbances caused by the drops hitting the water.

"This intriguing finding inspired us to look further," Ken Catania, a professor of biology at Vanderbilt, said in a press release. "For a variety of reasons, including the way that the spots are distributed around their body, we thought that the ISOs might be more than water ripple sensors."

In the Vanderbilt study, Leitch would use a minute hair designed to test human touch sensitivity to gently test the response of the animal's sensory domes, and found that the domes around the animals' teeth and jaws were more sensitive than human finger-tips.

“As soon as they feel something touch, they snap at it,” said Catania.

To inspect these touch receptors in more detail, Leitch and Catania used scanning electron microscopy to examine the skin and pigmented domes of American alligators. The researchers then sliced through several of the domes to inspect the sensory receptor structures and free nerve endings beneath. Leitch also stained the nerves surrounding the dome site so that he could trace them throughout the animal´s skin.

From their inspection, the scientists identified a diverse collection of "mechanoreceptors,” or nerves that respond to both pressure and vibration. They noted that some receptors are tuned specifically to the 20-35 Hertz range, an ideal range for sensing tiny water ripples.

The scientists theorized that this exceptional touch sensitivity, especially around the animals´ teeth and jaws, helps them to use their jaws in a refined manner. Female alligators and crocodiles have been observed delicately breaking open their eggs to assist their young in hatching. They have also been seen carrying hatchlings in their jaws. In light of the fact that these are the same jaws which can snap prey in half with a force greater than any other modern predator, the ISOs appear to be an important evolutionary development for the reptiles.